1. Field of the Invention
The invention relates to a syringe for the high pressure injection of fluid or paste products of the type where force is transmitted to a plunger via a lever which acts on a toothed rack incorporated into the plunger.
2. Brief Description of the Background of the Invention Including Prior Art
Syringes for high pressure injection of fluid or pasty products are known from French Patent Application No. 82/18546 where the force exerted by the user is transmitted to the plunger by a toothed rack multiplying force transmission. The syringe is comprised of a case with a forward area suitable for containing the product to be injected and a rear area, sealed at the back but with its forward end open to communicate with the forward area when the two are connected. A needle holding system or an ejector nozzle may be connected to the forward area. A toothed plunger rod is movably mounted in the case and can take any position between "loaded" when it is housed wholly in the rear area, and "injection completed" when it is housed wholly in the forward area, having discharged the product to be injected through either a needle or a nozzle. A forward-angled operating lever pivoting on pivots in the rear area moves a first ratchet, in opposition to a first flexible component, to exert a forward thrust on the toothed rack cut along the side of the plunger when pressure is exerted on the lever. A second ratchet, in concert with a second flexible component, co-operates with the toothed rack to prevent any backward motion. Means acting in opposition to this second elastic component are provided to free the rack from the second ratchet to allow the return of the plunger from "emptied" to the "loaded" position.
A known advantage of this system is the considerable multiplication of the pressure exerted on the lever by the user, which facilitates ejection of the product, normally requiring great effort either because of the fineness of the injection needle or the high viscosity of the paste product. However, the disadvantage exists that the considerable pressure exerted by the plunger on the product may attain a level such that one or another of the system components fails, either the tube containing the liquid bursts or the pivot pin of the lever buckles.